Enzyme-based regeneration of surface-attached nucleic acids is described herein. Microarrays involving hybridization of a probe to a target are important tools for genetic analysis. Conventionally, a microarray is used for a single analysis, after which it is discarded. The invention relates to a process for regeneration of a microarray through enzymatic digestion of a target from a surface-attached probe using a nuclease to digest a single strand of a nucleic acid duplex with directional specificity starting from the free end of the target strand. For example, a probe oligonucleotide bound to a gene chip at the 5'-end hybridizes to a target nucleic acid, leaving the 5' end of the target open to 5' 3' digestion. Lambda-exonuclease (.lamda.-exonuclease) cleaves single nucleotides from the 5' end of a duplex, progressing in the 5' 3' direction. Once the target strand is digested, the enzyme is rinsed from the microarray. The microarray is thus regenerated and ready for a subsequent use.